Selenium, though required only in minute quantities by the human body, is still a rather crucial trace mineral, for many central biochemical functions. These include promoting brain, nervous system activity, bolstering intrinsic defence mechanisms and regulating thyroid hormone synthesis, metabolism along with iodine.

Also Read: Iodine: Functions, Food Sources, Deficiency And Toxicity

Selenium is an element that occurs in two forms – inorganic salts as selenate and selenite, as well as organic complexes of selenocysteine and selenomethionine. The inorganic compounds are generally present in certain pockets of mineral-enriched soils, which is assimilated by the flora growing in that region. These plants then convert the inorganic selenium into organic components that carry the amino acids cysteine and methionine, besides their methylated byproducts.
Functions, food sources, deficiency and toxicity of selenium

The selenium needed for physiological tasks is present as inorganic and organic compounds, that are chiefly obtained from food, through dietary sources like mushrooms, nuts and seafood, or sometimes, via supplements. Of the two organic selenium types, selenomethionine is more abundant in the human system, being primarily concentrated in the skeletal and thyroid tissues. The other selenium variants, once ingested, are transformed to selenophosphate composites, for the biosynthesis of bodily proteins.

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Selenium is essential only in very small amounts in the diet, unlike other macro minerals like calcium and potassium. Nevertheless, it is important to ensure the daily requirement of selenium is supplied through food, for the smooth functioning of thyroid gland and hormones, the brain, as well as many other vital internal organs like heart, lungs and liver.

Also Read: Potassium: Functions, Food Sources, Deficiency And Toxicity


Being a crucial constituent of many biochemical complexes in cells and tissues, selenium carries out various bodily tasks by means of more than two dozen selenoproteins that control DNA synthesis. DNA i.e. Deoxyribonucleic Acid being the fundamental genetic material that influences the formation and function of cells, tissues and organs, selenium is highly essential for conserving overall health of the body.

Furthermore, selenium is involved in many significant processes, such as:

Promoting the cognitive abilities, memory, concentration, thinking, by positively influencing brain and nerve cell operations

Preserving reproductive wellness, fertility in both men and women

Safeguarding thyroid gland from undergoing oxidative stress and increasing the synthesis of thyroid hormones, for optimal growth, development, metabolism and immunity

Averting the onset of chronic ailments like cancer, diabetes, Alzheimer’s disease, by scavenging harmful free radicals circulating in the bloodstream

Contributing noteworthy antioxidant properties to flush out toxins in the system and lower the risk of heart disease, stroke

Decreasing volumes of harmful inflammatory compounds and raising levels of antioxidant glutathione peroxidase in the body, thereby augmenting cardiac functions and heart wellness

Enhancing lung power and lessening breathing problems, respiratory distress experienced in asthma

Food Sources:

The daily requirement of selenium intake is 55 micrograms for normal, healthy adults. There is a heightened necessity of selenium for gestating women, with the recommended daily quantities being 60 micrograms for the pregnancy period and 70 micrograms during the lactation phase.

Selenium is found in a plethora of plant and animal sources. The plant-based food sources contain ample quantities of the mineral, particularly when grown in soils loaded with selenium.

Some of the numerous dietary sources of selenium include:

Whole grains like brown rice, oats and barley

Nuts such as brazil nuts, almonds, pistachios

Beans and legumes like chickpeas, kidney beans

Dairy products comprising milk, cheese, yoghurt

Seafood like tuna, shellfish, halibut

Eggs, chicken and animal meat produce

Mushrooms and garlic


Since selenium is necessary for carrying out many vital bodily functions, a deficiency in the mineral results in many complications. A daily intake of fewer than 55 micrograms of selenium over a long period of time can hamper thyroid functioning, as well as lead to a decline in mental capabilities and immunity.

Moreover, it can also prompt symptoms of the sudden loss of hair, feeling of exhaustion and fatigue, weakness in muscles, slowing down of energy metabolism and even result in infertility in men and women.


Selenium can be tolerated in the body for a daily intake of a maximum quantity of 400 micrograms, in healthy adults. In the majority of cases, toxic levels of selenium in the body arise very rarely, being triggered mostly by an overdose of concentrated supplements and seldom due to dietary food sources.

Aside from a lingering bad mouth odour with a metallic taste, selenium toxicity can cause many grave consequences in the system. These consist of nervous system malfunctioning, skin infections, excessive hair fall, damage to teeth, fragile, brittle nails. In very extreme instances, toxic doses of selenium can even lead to heart attacks, kidney failure or be fatal.

It is hence always advised to consult with a doctor before consuming selenium supplements and follow a healthy, balanced diet with selenium-rich foods as much as possible, to ensure adequate intake of the vital nutrient.